Casing and tubing

Casing and tubing strings are the main parts of the well construction. All wells drilled for the purpose of oil or gas production (or injecting materials into underground formations) must be cased with material with sufficient strength and functionality.

1.💠Casing
Casing is the major structural component of a well. Casing is needed to:
🔹Maintain borehole stability
🔸Prevent contamination of water sands
🔹Isolate water from producing formations
🔸Control well pressures during drilling, production, and workover operations

Casing provides locations for the installation of:
🔹Blowout preventers
🔸Wellhead equipment
🔹Production packers
🔸Production tubing

The cost of casing is a major part of the overall well cost, so selection of casing size, grade, connectors, and setting depth is a primary engineering and economic consideration.

2.💠Casing strings
There are six basic types of casing strings:
🔹Conductor Casing
🔸Surface Casing
🔹Intermediate Casing
🔸Production Casing
🔹Liner
🔸Liner tieback casing

3.💠Tubing
Tubing is the conduit through which oil and gas are brought from the producing formations to the field surface facilities for processing. Tubing must be adequately strong to resist loads and deformations associated with production and workovers. Further, tubing must be sized to support the expected rates of production of oil and gas. Clearly, tubing that is too small restricts production and subsequent economic performance of the well. Tubing that is too large, however, may have an economic impact beyond the cost of the tubing string itself, because the tubing size will influence the overall casing design of the well.

4.💠Properties of casing and tubing
The American Petroleum Inst. (API) has formed standards for oil/gas casing that are accepted in most countries by oil and service companies. Casing is classified according to five properties:
🔹The manner of manufacture
🔸Steel grade
🔹Type of joints
🔸Length range
🔹The wall thickness